docs: record capture schema

CHANGELOG.md

@@ -27,6 +27,8 @@
   experiment.
 - Capture poses must now contain proper rigid rotations, rejecting invertible
   scale/shear transforms that would silently corrupt multi-view fusion.
+- Added `CAPTURE_MANIFEST_SCHEMA.md` with a copyable calibrated-capture example,
+  coordinate conventions, and the held-out-view workflow.
 - Extended the deterministic benchmark with a support-pruning ablation that
   records how many fused voxels remain supported by at least two input views.